Studies in patients with primary aldosteronism have been directed toward improvement of techniques for diagnosis and understanding the pathophysiology of the disorder. As primary aldosteronism may be produced by either bilateral adrenal hyperplasia or by unilateral adenoma, a distinction between the two adrenal abnormalities is necessary because patients with hyperplasia respond poorly to operation. The response of plasma adrenal corticosteroids to postural change, computed tomography of the adrenal glands and selective adrenal vein sampling for determination of adrenal corticosteroids are the diagnostic modalities currently under evaluation for their usefulness in identification of patients with primary aldosteronism caused by an aldosterone-producing adenoma. The results to date indicate that selective adrenal vein sampling is the most reliable technique for evaluation of adrenal function in primary aldosteronism. The effects of an overproduction of aldosterone on the production of prostaglandins by the kidney and the effects of treatment with a prostaglandin synthetase inhibitor on renal function and on adrenal steroid biogenesis in patients with primary aldosteronism are also under study.